1. Field of the Invention
The present invention relates to an iris apparatus (diaphragm apparatus) which can be advantageously used for a diaphragm or a shutter of a camera.
2. Description of the Related Art
In a conventional diaphragm apparatus of a camera, a plurality of shutter blades are circumferentially arranged and held between stationary and movable circular rings; wherein the amount of overlapping of the shutter blades is varied to thereby vary the diameter of a central aperture defined by the shutter blades when the movable ring is rotated in the circumferential direction. To this end, the number of the components, including: the shutter blades, the stationary and movable rings, and a mechanism which moves the diaphragm, is increased; and consequently, it is difficult to make the diaphragm apparatus small. In particular, in recent digital cameras using CCD image pickup devices, it is necessary not only to miniaturize the camera body, but also the photographing lens system in order to correspond with the extremely small CCD image pickup device. Accordingly, it is necessary for the diaphragm apparatus and the shutter device to be made smaller. Furthermore, the speed of the movement of a mechanical operation is limited. For example, in the case of a diaphragm shutter in which the diaphragm is used also for a shutter, it is difficult to carry out a photographing operation at high speed. In addition, in the conventional diaphragm apparatus, since the aperture is defined by shutter blades, the aperture is of a polygonal shape determined in accordance with the number of the shutter blades; and hence blur-spot of an object image picked up by the camera is polygonal, thus resulting in deteriorated image quality.
As mentioned above, in the conventional diaphragm apparatus, from the mechanical viewpoint, the number of the elements is increased, making it difficult to make the diaphragm apparatus small, and difficult to increase the speed of the mechanical operation. Moreover, from the viewpoint of the photographing operation, an image in an out-of-focus state is polygonal, whereby a high quality image cannot be obtained. In addition to, if the diaphragm apparatus is driven by a power source such as a battery, the power consumption is increased due to the large mechanical load necessary to simultaneously move the plural shutter blades, thus leading to a reduced service life of the battery. The problem with the increased power consumption is especially serious, taking into account the miniaturization of the camera in which the battery capacity is reduced.